Invasive ultrasound imaging catheters are designed for use in conjunction with a guide wire. In the past, four different methods have been used to adapt the imaging catheter to a guide wire.
In the first method a guide wire tip is attached to the distal end of an imaging sheath and is known as a "fixed wire" design. This method has been used with mechanically rotated probes. The design, however, has two disadvantages, first, the wire cannot be left across a lesion while the imaging catheter is withdrawn and replaced with a different device, and secondly, fixed wire devices are more difficult to "steer" than the common "steerable" and "removable" guide wires. An example of a fixed wire tip is disclosed in U.S. Pat. No. 4,794,931--Yock.
A second type of catheter, known as transducer-array catheters, have been designed so that a guide wire can be threaded through a lumen which passes coaxially through the array. This design allows a user to place the imaging catheter over a guide wire by the same methods practiced with standard dilatation catheters. Transducer array catheters work with electronically scanned transducer arrays however this type of catheter design cannot be adapted for use with mechanically-rotated probes. An example of a transducer-array catheter is disclosed in U.S. Pat. No. 4,917,097--Proudian et al.
The third catheter design uses a dual lumen sheath. A lumen for the guide wire and a parallel lumen for a rotating ultrasound probe are provided. Unfortunately, the side-by-side positioning of the wire and probe lumens causes the catheter to be of a larger cross-section than is necessary for ultrasound imaging. Large catheters are disadvantageous because they reduce or stop blood flow in small or narrowed arteries. A product of this type is sold by Cardiovascular Imaging Systems, Inc. of Mountain View, Calif. (USA).
Finally, a fourth design for this type of catheter provides a single-lumen sheath positioned over a guide wire and across the section of the vessel to be imaged. The wire is then removed and "replaced" with an ultrasound probe. This design has the advantage of yielding a catheter diameter which is not much larger than the probe diameter. However, using the single-lumen sheath in conjunction with "over-the-wire" catheters is time consuming. For example, to remove the ultrasound catheter and position a dilatation catheter a user would first remove the probe, then position the guide wire and remove the sheath. Finally, the user would place the dilatation catheter over the wire. In contrast, a user can exchange one dilatation catheter for another by removing the first catheter and placing the second catheter over the wire. The time difference can be very important when working within the coronary arteries. An example of this type of device is sold by InterTherapy, Inc. of Santa Ana, Calif. (USA).
Thus, it can be seen that there is a long-felt yet unfilled need to provide a design which permits a catheter containing a mechanically rotated probe to be steered into place using a guide wire while maintaining a minimum cross-section.